The fitness industry has long desired a stationary, low-impact, exercise machine capable of adapting and conforming to a user's natural gait, stride and pace (hereinafter “user conforming exercise machine”) during exercise. Treadmills accommodate user-defined gait and stride (i.e., uncontrolled path of travel), but are high-impact with machine-dictated pace. Elliptical exercise machines are low-impact and accommodate user-defined pace, but have machine-dictated gait and stride (i.e., defined path of travel).
Several attempts have been made to achieve a user-conforming exercise machine by employing leg linkages that mimic human legs (i.e., an exercise machine having a stationary frame supporting a pair of leg linkages with each leg linkage having (i) an upper link pivotally coupled proximate its upper end to the frame, (ii) a lower link pivotally coupled proximate its upper end to the lower end of the upper link, and (iii) a foot support on the lower end of each lower link). Exemplary lower body mimetic stationary exercise machines are depicted and described in U.S. Pat. Nos. 5,290,211, 5,499,956, 5,735,773, 5,911,649, 6,036,622, 6,045,487, 6,152,859 (FIG. 29), U.S. Pat. Nos. 7,645,215, 7,833,134, 8,109,861, and 8,409,058, the disclosures of which are hereby incorporated by reference. While constituting a significant advance towards achieving a user-conforming exercise machine, these lower body mimetic stationary exercise machines have met with limited commercial success as they exert active and reactive forces that do not coordinate well with a user's innately anticipated natural interaction with the environment during walking or running.
Accordingly, a need continues to exist for a stationary user-conforming exercise machine that ergonomically conforms to the natural innate striding motion of the user.